论文标题
固体$^4 $ He中的非线性和障碍超声传播：脱位线和固定杂质的动态
Nonlinear and Hysteretic Ultrasound Propagation in Solid $^4$He: Dynamics of Dislocation Lines and Pinning Impurities
论文作者
论文摘要
我们报告了9.6 MHz超声传播的测量值，低至15 MK polycrystalline Quantum solid $^4 $ HE，其中含有0.3和20 ppm $^3 $ He Insigurity。超声的衰减和速度受到错位振动的强烈影响。观察到的衰减从1.2 K到附近0.3 K附近的峰值增加与驱动振幅无关，并且反映了从阻尼到阻尼不足的脱位脱位固定在网络节点上的振荡。低于0.3 K，在衰减和速度下都观察到振幅依赖性和滞后变化。衰减从0.3 K时的峰值下降至非常小的恒定值以低于70 mk的速度，在足够低的超声驱动幅度下，其在最高驱动幅度下仍保持高值降至15MK。低驱动振幅下的行为可以通过杂质对位错的脱位和脱位的影响很好地描述。位错线和$^3 $ HE原子之间的结合能估计为0.35K。在中间驱动振幅下的非线性和滞后行为是根据压力诱导的未固定的分析，这可能会在网络脱位段内发生灾难性。固定在15 mk的放松时间很短（$ <4 $ s），而未锁定需要超过1,000 s。
We report on the measurements of 9.6 MHz ultrasound propagation down to 15 mK in polycrystalline quantum solid $^4$He containing 0.3 and 20 ppm $^3$He impurities. The attenuation and speed of ultrasound are strongly affected by the dislocation vibration. The observed increase in attenuation from 1.2 K to a peak near 0.3 K is independent of drive amplitude and reflects crossover from overdamped to underdamped oscillation of dislocations pinned at network nodes. Below 0.3 K, amplitude-dependent and hysteretic variations are observed in both attenuation and speed. The attenuation decreases from the peak at 0.3 K to a very small constant value below 70 mK at sufficiently low drive amplitudes of ultrasound, while it remains a high value down to 15mK at the highest drive amplitude. The behaviors at low drive amplitudes can be well described by the effects of the thermal pinning and unpinning of dislocations by the impurities. The binding energy between a dislocation line and a $^3$He atom is estimated to be 0.35 K. The nonlinear and hysteretic behaviors at intermediate drive amplitudes are analyzed in terms of stress-induced unpinning which may occur catastrophically within a network dislocation segment. The relaxation time for pinning at 15 mK is very short ($< 4$ s), while more than 1,000 s is required for unpinning.
